Cutting elements, such as shear cutter type cutting elements used in rock bits or other cutting tools, typically have a body (i.e., a substrate) and an ultra hard material. The ultra hard material forms the cutting surface of the cutting element, and the substrate is typically provided for the purpose of attaching the ultra hard material to the cutting tool. The substrate is generally made from tungsten carbide-cobalt (sometimes referred to simply as “cemented tungsten carbide,” “tungsten carbide” or “carbide”). The ultra hard material layer is a polycrystalline ultra hard material, such as polycrystalline diamond (“PCD”), polycrystalline cubic boron nitride (“PCBN”) or thermally stable product (“TSP”) such as thermally stable polycrystalline diamond. The ultra hard material provides a high level of wear and/or abrasion resistance that is greater than that of the metallic substrate.
The PCD material is formed by a known process in which diamond crystals are mixed with a catalyst material and sintered with a substrate at high pressure and high temperature. Catalyst from the substrate also infiltrates the diamond crystals during the sintering process. This sintering process creates a polycrystalline diamond structure having a network of intercrystalline bonded diamond crystals, with the catalyst material remaining in the voids or gaps between the bonded diamond crystals. The catalyst material facilitates and promotes the inter-crystalline bonding. The catalyst material is typically a solvent catalyst metal from Group VIII of the Periodic table (CAS version of the periodic table in the CRC Handbook of Chemistry and Physics), such as cobalt. However, the presence of the catalyst material in the sintered PCD material introduces thermal stresses to the PCD material, when the PCD material is heated, as for example by frictional heating during use, as the catalyst typically has a higher coefficient of thermal expansion than does the PCD material. Thus, the sintered PCD is subject to thermal stresses, which limit the service life of the cutting element. Furthermore, when the operating or servicing temperature reaches or exceeds 700° C., the diamond structure in the PCD layer converts back to graphite with the presence of Group VIII catalyst material, causing structural disintegration in the PCD layer.
To address this problem, the catalyst is substantially removed from the PCD material, such as by leaching, in order to create TSP. For example, one known approach is to remove a substantial portion of the catalyst material from at least a portion of the sintered PCD by subjecting the sintered PCD construction to a leaching process, which forms a TSP material portion substantially free of the catalyst material. The entire PCD layer can be subjected to this leaching process to remove the catalyst material. If the PCD material is attached to a substrate, the substrate and the PCD material can be separated from each other either before or after the leaching process.
After the TSP material has been formed, it is bonded onto a substrate in order to form a cutting element. During this bonding process, the TSP material and substrate are subjected to heat and pressure. An infiltrant material (such as cobalt from the substrate) infiltrates the TSP material, moving into the voids (i.e., the interstitial spaces) between the bonded crystals, previously occupied by the catalyst material. Other metal or metal alloy or non-metallic infiltrants may be used in addition to or instead of cobalt from the substrate. After bonding, the infiltrant(s) can be removed from a portion of the infiltrated TSP material. For example, the infiltrant can be leached from the cutting surface of the infiltrated TSP (opposite the substrate) to remove the infiltrant materials in order to create a thermally stable cutting surface, while retaining the infiltrant in the portion of the infiltrated TSP closer to the substrate, in order to retain a strong bond between the diamond layer and the substrate.
During the catalyst removing step, when the catalyst material is removed from the PCD to form TSP, some residual materials are left behind in the voids between the diamond crystals. Some residuals may be, for example, the residual cobalt carbides in the voids not completely digested by the leaching agent, and corresponding oxides forming afterwards. The presence of these residuals hinders the infiltration of cobalt (or other infiltrant) into the TSP during bonding. Additionally, gases, moisture, and residual leaching agent occupy the voids between the diamond crystals. These gases, moisture, oxides, and other residuals inhibit the infiltration of the infiltrant into the TSP material, as they exert a force against the infiltrant material that is moving into the TSP.
The result is TSP material that is only partially infiltrated or not properly infiltrated, as the infiltration path is blocked by those residual materials. Partial infiltration is problematic, as thermal and other stresses build in the non-infiltrated region of the TSP. Partial infiltration also makes leaching more difficult, and weakens the bond between the TSP layer and the substrate. Partial infiltration also creates inconsistencies in the performance of the TSP cutting elements. Accordingly, there is a need for a system and method for forming TSP material that facilitates infiltration during bonding, and improves the thermal characteristics of the material.